Magma: an enabled scissor test over a never-written box clips nothing instead of everything (DefaultScissorFollowsSurfaceScenario runs on DirectVulkan instead of skipping).

MobileGL/MG_Backend/DirectVulkan/Renderer/VulkanRenderer.cpp

@@ -670,6 +670,18 @@ namespace MobileGL::MG_Backend::DirectVulkan {
         vkCmdSetLineWidth(commandBuffer, lineWidth);
     }
 
+    // Whether the GL scissor test clips viewport index `index`. The scissor rectangles start
+    // all-zero, and all-zero there means "never written" (RenderState's constructor), not an
+    // empty box: GL's initial box is the whole window, so until the application's first
+    // glScissor an enabled test clips nothing. Read as a box it would clip EVERYTHING, so every
+    // reader of the box asks this first. The resolution matches the viewport's (ComputeGLViewport
+    // resolves a never-written viewport to the current framebuffer's extent).
+    static Bool GLScissorTestClips(Uint32 index = 0) {
+        const RenderStateParameters& parameters = MG_Pipe::gPipeInputs.GetRenderStateParameters();
+        const Uint32 bit = 1u << index;
+        return (parameters.ScissorTestEnabledMask & bit) != 0 && (parameters.ScissorBoxWrittenMask & bit) != 0;
+    }
+
     static VkRect2D MakeClampedScissorRect(const IntVec4& scissorBox, const IntVec2& framebufferExtent) {
         const Int x0 = std::max<Int>(0, scissorBox.x());
         const Int y0 = std::max<Int>(0, scissorBox.y());
@@ -3393,7 +3405,7 @@ namespace MobileGL::MG_Backend::DirectVulkan {
                                                   VkSurfaceTransformFlagBitsKHR preTransform,
                                                   Bool isDefaultFbo) const {
         const auto& parameters = MG_Pipe::gPipeInputs.GetRenderStateParameters();
-        if ((parameters.ScissorTestEnabledMask & (1u << index)) == 0) {
+        if (!GLScissorTestClips(index)) {
             VkRect2D full{};
             full.offset = {0, 0};
             full.extent = {static_cast<Uint32>(extent.x()), static_cast<Uint32>(extent.y())};
@@ -3515,7 +3527,7 @@ namespace MobileGL::MG_Backend::DirectVulkan {
                 key.stencilWriteMask[face] = p.StencilStates[face].WriteMask;
                 key.stencilRef[face] = p.StencilStates[face].Ref;
             }
-            key.scissorEnabled = (p.ScissorTestEnabledMask & 1u) != 0;
+            key.scissorEnabled = GLScissorTestClips(0);
             key.scissorBox[0] = p.ScissorBoxes[0].x();
             key.scissorBox[1] = p.ScissorBoxes[0].y();
             key.scissorBox[2] = p.ScissorBoxes[0].z();

MobileGL/MG_Backend/DirectVulkan/Renderer/WireDraw.inc

@@ -1046,7 +1046,7 @@
         if (count == 0) return remaining & ~handled;
 
         VkRect2D area{{0, 0}, {key.width, key.height}};
-        if (MG_Pipe::gPipeInputs.IsCapabilityEnabled(CapabilityInput::ScissorTest)) {
+        if (GLScissorTestClips()) {
             const auto& box = MG_Pipe::gPipeInputs.GetScissorBox();
             const Int32 x0 = std::max(box.x(), 0), y0 = std::max(box.y(), 0);
             const Int32 x1 = std::min(box.x() + box.z(), static_cast<Int32>(key.width));

MobileGL/MG_Backend/DirectVulkan/Renderer/WireFramebuffer.inc

@@ -369,7 +369,7 @@
         const VkCommandBuffer passBuffer = active->commandBuffer;
         const Uint64 passHash = active->hash;
         VkRect2D area{{0, 0}, {key.width, key.height}};
-        if (MG_Pipe::gPipeInputs.IsCapabilityEnabled(CapabilityInput::ScissorTest)) {
+        if (GLScissorTestClips()) {
             const auto& box = MG_Pipe::gPipeInputs.GetScissorBox();
             const Int32 x0 = std::max(box.x(), 0), y0 = std::max(box.y(), 0);
             const Int32 x1 = std::min(box.x() + box.z(), static_cast<Int32>(key.width));
@@ -469,7 +469,7 @@
             const ClearAttachmentPayload& payload, GLint drawbuffer) {
         GLbitfield remaining = payload.mask & (GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT);
         if (!remaining || fbo.IsDefault || drawbuffer >= 0 || m_wirePreparationDepth != 0) return remaining;
-        const Bool scissor = MG_Pipe::gPipeInputs.IsCapabilityEnabled(CapabilityInput::ScissorTest);
+        const Bool scissor = GLScissorTestClips();
         const auto wholeImage = [&](const WireImage& image) {
             if (!scissor) return true;
             const auto& box = MG_Pipe::gPipeInputs.GetScissorBox();
@@ -614,7 +614,7 @@
             if (!image.image) return;
             m_textureManager->FlushPendingUploads();
             VkRect2D area{{0, 0}, image.extent};
-            if (MG_Pipe::gPipeInputs.IsCapabilityEnabled(CapabilityInput::ScissorTest)) {
+            if (GLScissorTestClips()) {
                 const auto& box = MG_Pipe::gPipeInputs.GetScissorBox();
                 const Int32 x0 = std::max(box.x(), 0), y0 = std::max(box.y(), 0);
                 const Int32 x1 = std::min(box.x() + box.z(), static_cast<Int32>(image.extent.width));
@@ -1263,7 +1263,7 @@
         RetireWireDrawPass();
         // The scissor test clips blit writes: intersect the destination rectangle with
         // the scissor box and shrink the source proportionally.
-        if (MG_Pipe::gPipeInputs.IsCapabilityEnabled(CapabilityInput::ScissorTest)) {
+        if (GLScissorTestClips()) {
             const IntVec4& scissor = MG_Pipe::gPipeInputs.GetScissorBox();
             const auto clipAxis = [](GLint& d0, GLint& d1, GLint& s0, GLint& s1, GLint clipLo, GLint clipHi) -> Bool {
                 const Bool dstFlipped = d1 < d0;

MobileGL/MG_IntegrationTest/Scenarios/DefaultScissorFollowsSurfaceScenario.cpp

@@ -13,7 +13,9 @@
 // keeps the surface size in a memo that a swap, a change of draw surface, or a surface's creation
 // or destruction invalidates. This case makes a second, larger surface current on the same
 // context and clears it with the scissor test on: the clear must reach the larger surface's far
-// corner, which a size remembered from the first surface would cut off.
+// corner, which a size remembered from the first surface would cut off. DirectVulkan resolves a
+// never-written box to the whole framebuffer it draws into, so the same clear reaches the corner
+// there too (it used to read the all-zero box as an empty one and clear nothing).
 
 #include <array>
 
@@ -36,7 +38,6 @@ class DefaultScissorFollowsSurfaceScenario : public ScenarioTest {};
 
 TEST_F(DefaultScissorFollowsSurfaceScenario, AClearOnALargerSurfaceMadeCurrentReachesItsFarCorner) {
     if (!Ready() || IsSkipped()) return;
-    if (Gl().BackendName() != "DirectGLES") GTEST_SKIP() << "the substituted scissor box is DirectGLES's";
     const EGLDisplay display = eglGetCurrentDisplay();
     const EGLSurface first = eglGetCurrentSurface(EGL_DRAW);
     const EGLContext context = eglGetCurrentContext();